The present invention relates to abrasive filaments, methods of making the abrasive filaments and methods of refining a surface with the abrasive filaments. The abrasive filaments comprise a thermoplastic matrix and plastic abrasive particles.
Polyamide, also known as xe2x80x9cNylonxe2x80x9d, filaments were developed in the late 1950""s as a synthetic alternative to natural filaments. At about that time an extrusion process was developed for dispersing abrasive particles uniformly in a nylon matrix in the form of a filament (U.S. Pat. Nos. 3,522,342 and 3,947,169). A review of polyamide abrasive filaments is presented by Watts, J. H., xe2x80x9cAbrasive Monofilaments-Critical Factors that Affect Brush Tool Performancexe2x80x9d, Society of Manufacturing Engineers Technical Paper, 1988, a written version of a presentation by the author at the WESTEC Conference, held Mar. 21-24, 1988. It is known to use conventional inorganic abrasive particles with such polyamide filaments. As explained by Watts, as filaments of this type wear, new abrasive particles are exposed. An abrasive filament brush tool made using a plurality of these filaments is thus regenerated during use.
While adequate for many purposes, various polyamides have property limitations which make their use less than optimal for certain applications of abrasive filaments. U.S. Pat. No. 5,427,595, Pihl et al., addresses such limitations and describes the use of thermoplastic elastomers in abrasive filaments to reduce or overcome such limitations. The filaments of Pihl et al. include a core component and a sheath component which are coextruded. Either or both of the core and sheath includes abrasive particles adhered therein. Pihl et al. teaches the use of conventional inorganic abrasive particles, although the claims of Pihl et al. are not limited to any particular type of abrasive particle.
U.S. Pat. No. 5,460,883, Barber, Jr., et al., also addresses the limitations of polyamides and describes the use of thermoplastic elastomers in abrasive filaments to reduce or overcome such limitations. The filaments of Barber et al. include a preformed core component and a sheath component coated onto the core to form a composite filament. The coated sheath includes abrasive particles adhered therein. Barber et al. teaches the use of conventional inorganic abrasive particles, although the claims of Barber et al. are not limited to any particular type of abrasive particle.
Brushes incorporating abrasive bristles or filaments have been used for many years to polish, clean and abrade a wide variety of substrates. These brush products typically have a plurality of bristles or filaments that contact the substrate. Abrasive particles can be added to bristles to increase their abrasiveness. The brushes may be made as follows. A mixture of abrasive particles and any suitable thermoplastic binder may be combined and then extruded to form a bristle or abrasive filament. The abrasive filament is then cut to the desired length. A plurality of these abrasive filaments are then mechanically combined to form a brush segment. Next, a plurality of these brush segments may be installed on a hub or plate to form a brush.
The abrasive particles typically employed in abrasive filaments and brushes described above have been limited to inorganic particles which necessarily have a high hardness, e.g. greater than 7 and usually greater than 9 on the Mohs hardness scale. The abrasive particles are sufficiently temperature resistant so as not to be deleteriously affected by the bristle or filament manufacturing process. Such abrasive particles are used in abrasive filaments and brushes to refine the surface of a workpiece. In some instances, this refinement is to remove a portion of the workpiece. In other instances, this refinement is to remove unwanted material (e.g., debris, oil residue, oxide layer, paint, etc.) from the workpiece surface. In some applications, it is desired to remove this unwanted material without any removal or abrasion of the underlying workpiece. However the abrasive particles in the abrasive filaments can be so xe2x80x9caggressivexe2x80x9d that the abrasive filaments remove the unwanted material along with the workpiece surface.
U.S. Pat. Nos. 3,090,061 and 3,134,122 to Charvat disclose the use of plastic beads on hard wire bristles to maintain the desired spacing of the bristles when assembled into a brush. Charvat teaches that this is effective to properly space and control the bristles to prevent undue compacting of the brush face and to assure equal frequency of tip contacts per unit length of brush face. The preferred brush bristle taught by Charvat is a steel wire have a Knoop hardness of at least 600, and in some cases in excess of 700 and even in excess of 800. Charvat also teaches that the bristle material may comprise any suitable brush bristle, including nylon and glass filament bristles, and that the beads need not be apertured bodies on the bristles, but may be spaced globules and protuberances adhered to the bristles which are not necessarily concentric therewith. The plastic beads and bristles are coated with a thin plastic coating. Charvat does not teach or suggest that the plastic bead spacer or buffer can instead be used as an abrasive particle. In fact, Charvat teaches the use of bristle materials that are much harder and more abrasive than the plastic beads, and also suggests including conventional inorganic abrasive particles in the plastic beads. Charvat teaches that the plastic coating and beads will erode during operation and that the protruding bristle ends are adapted to operate on the work in the manner of a true brush.
What is desired is a filament having abrasive particles that can remove a foreign material from a workpiece surface efficiently without any damage to the underlying workpiece, or provide a desired fine finish to the workpiece surface, and in which the abrasive particles are sufficiently durable to withstand the filament manufacturing process.
This invention pertains to novel abrasive filaments including plastic abrasive particles, brush constructions containing such abrasive filaments, methods of making such abrasive filaments, and methods of refining a workpiece surface using the brush construction.
One embodiment pertains to an abrasive filament, comprising plastic abrasive particles interspersed in a thermoplastic matrix. In one preferred embodiment of the abrasive filament, the plastic abrasive particles have a greater hardness than the thermoplastic matrix
Regarding this first embodiment, there are four major types of abrasive filaments. In the first type, the plastic abrasive particles are interspersed nearly uniformly and preferably uniformly throughout the thermoplastic matrix. In this first type, this results in a substantially homogeneous abrasive filament. In the second, third and fourth types, the abrasive filament comprises a sheath and a core. In the second type, the sheath comprises the thermoplastic matrix having the plastic abrasive particles interspersed throughout at least a portion thereof The core can comprise either a second thermoplastic material coextruded with the sheath, or a preformed core having the sheath coated over it. In the third type, the core comprises the thermoplastic matrix having the plastic abrasive particles interspersed throughout at least a portion thereof and the sheath comprises a second thermoplastic material. In the fourth type, the sheath and core both comprise a thermoplastic matrix having plastic abrasive particles interspersed throughout at least a portion thereof In these four embodiments, either the thermoplastic matrix and/or the plastic abrasive particles may be different between the sheath and core.
The term xe2x80x9cinterspersedxe2x80x9d means that the abrasive particles are embedded within and located throughout the thermoplastic material that forms the filament. In the case of the core/sheath embodiments, xe2x80x9cinterspersedxe2x80x9d means that the abrasive particles are embedded within and located throughout the thermoplastic matrix that forms the core or sheath, or both, as appropriate. The particles are interspersed so as to create a substantially homogenous distribution, though not necessarily an absolutely homogenous distribution. Furthermore, while the majority of the particles are wholly embedded within the thermoplastic matrix, this not preclude the possibility of having some exposed particles at the surface that extend partially outside of the thermoplastic matrix.
The term xe2x80x9cthermoplastic matrixxe2x80x9d means that the material is capable of being heated to a molten state and then subsequently cooled to a solid state. The thermoplastic matrix can be any thermoplastic polymer or thermoplastic elastomer. Examples of thermoplastic polymers suitable for this invention include polycarbonate, polyetherimide, polyester, polyethylene, polysulfone, polystyrene, acrylonitrilebutadienestyrene block copolymer, polypropylene, acetal polymers, polyurethanes, polyamides and combinations thereof Examples of thermoplastic elastomers useful in the present invention include polyester elastomers, polyurethane elastomers, polyamide elastomers, and silicone elastomer/polyamide block copolymeric, with the low and high equivalent weight polyfunctional monomers selected appropriately to produce the respective thermoplastic matrix.
xe2x80x9cThermoplastic elastomersxe2x80x9d as used herein, refers to the class of polymeric substances which combine the processability (when molten) of thermoplastic materials with the functional performance and properties of conventional thermosetting rubbers (when in their non-molten state), and which are described in the art as ionomeric, segmented, or segmented ionomeric thermoplastic elastomers. The segmented versions comprise xe2x80x9chard segmentsxe2x80x9d which associate to form crystalline hard domains connected together by xe2x80x9csoftxe2x80x9d, long, flexible polymeric chains. The hard domain has a melting or disassociation temperature above the melting temperature of the soft polymeric chains.
The term xe2x80x9csegmented thermoplastic elastomerxe2x80x9d, as used herein, refers to the sub-class of thermoplastic elastomers which are based on polymers which are the reaction product of a high equivalent weight polyfunctional monomer and a low equivalent weight polyfunctional monomer.
Segmented thermoplastic elastomers are preferably the condensation reaction product of a high equivalent weight polyfunctional monomer having an average functionality of at least 2 and an equivalent weight of at least about 350, and a low equivalent weight polyfunctional monomer having an average functionality of at least about 2 and an equivalent weight of less than about 300. The high equivalent weight polyfunctional monomer is capable on polymerization of forming a soft segment, and the low equivalent weight polyfunctional monomer is capable on polymerization of forming a hard segment. Segmented thermoplastic elastomers useful in the present invention include segmented polyester thermoplastic elastomers, segmented polyurethane thermoplastic elastomers, segmented polyurethane thermoplastic elastomers blended with other thermoplastic materials, segmented polyamide thermoplastic elastomers, ionomeric thermoplastic elastomers, and silicone elastomer/polyamide block copolymeric, with the low and high equivalent weight polyfunctional monomers selected appropriately to produce the respective thermoplastic matrix.
The segmented thermoplastic elastomers preferably include xe2x80x9cchain extendersxe2x80x9d, low molecular weight (typically having an equivalent weight less than 300) compounds having from about 2 to 8 active hydrogen functionality, which are known in the art. Particularly preferred examples include ethylene diamine and 1,4-butanediol.
xe2x80x9cIonomeric thermoplastic elastomersxe2x80x9d refers to a sub-class of thermoplastic elastomers based on ionic polymers (ionomers). Ionomeric thermoplastic elastomers are composed of two or more flexible polymeric chains bound together at a plurality of positions by ionic associations or clusters, each ionic cluster being analogous to a hard crystalline domain in a elastomers comprising segmented polymers. The ionomers are typically prepared by copolymerization of a functionalized monomer with an olefinic unsaturated monomer, or direct functionalization of a preformed polymer. Carboxyl-functionalized ionomers are obtained by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene, and similar comonomers by free-radical copolymerization. The resulting copolymer is generally available as the free acid, which can be neutralized to the degree desired with metal hydroxides, metal acetates, and similar salts.
Blends of thermoplastic elastomers and thermoplastic materials are also within the invention, allowing even greater flexibility in tailoring mechanical properties of filaments of the invention.
As used herein, the term xe2x80x9chardenedxe2x80x9d refers to the physical state of the thermoplastic materials when the temperature of the thermoplastic polymer or thermoplastic elastomer is below the melting or dissociation temperature. The term can also be used to describe the room temperature (i.e. about 10 to about 40xc2x0 C.) hardness (Shore D scale) of the thermoplastic material. It is preferred that the room temperature Shore D durometer hardness of the thermoplastic materials used in the invention be at least about 30, more preferably ranging from about 30 to about 90, as determined by ASTM D790. The term is not meant to include physical and/or chemical treatment of the thermoplastic matrix or thermoplastic elastomer/plastic abrasive particle mixture to increase its hardness.
The term xe2x80x9cplastic abrasive particlesxe2x80x9d means that there are discrete entities or particulates present in the thermoplastic matrix. The term xe2x80x9cplasticxe2x80x9d means that the abrasive particles are formed from an organic material. It is preferred that the particles be formed from either a thermosetting or thermoplastic polymer. Examples of such plastic abrasive particles include polypropylene, polyester, polycarbonate, polystyrene, methacrylate, methylmethacrylate, and polyvinylchloride. Still other examples of plastic abrasive particles include the crosslinked polymers of phenolic, epoxy, ureaformaldehyde, acrylate, and melamine-formaldehyde based materials.
xe2x80x9cPreformed corexe2x80x9d, as used herein, means one or more core elements which is formed in a step separate from and prior to one or more coating steps, one of which coats the preformed core with thermoplastic sheath; in other words, a preformed core is not made simultaneously with the hardened composition. The cross-section of the preformed core is not limited as to shape; however, preformed cores having substantially round or rectangular cross-sections have been found suitable.
The preformed core preferably extends through the entire length of the filament, but this is not required. It is also not required that the preformed core cross-section have the same cross-section as the overall filament, and the preformed core and hardened composition can be concentric or eccentric, with a single or plurality of core elements being within the invention.
The preformed core can be continuous individual metallic wires, a multiplicity of continuous individual metallic wires, a multiplicity of non-metallic continuous filaments, or a mixture of the latter two, provided that the melting temperature of the preformed core is sufficiently high so that a coating of abrasive-filled molten thermoplastic can be applied to at least a portion of the preformed core, and the molten thermoplastic cooled rapidly enough to maintain the integrity of the preformed core.
Preferred preformed cores include single and multistranded metallic cores, e.g., plain carbon steels, stainless steels, and copper. Other preferred preformed cores include a multiplicity of non-metallic filaments e.g., glass, ceramics, and synthetic organic polymeric materials such as aramid, polyamide, polyester, and polyvinyl alcohol.
The second embodiment pertains to an abrasive brush construction, comprising a plurality of abrasive filaments having plastic abrasive particles.
In one form of this embodiment, the abrasive brush comprises:
(a) a plurality of abrasive filaments, at least a portion of which comprise a thermoplastic matrix and plastic abrasive particles distributed in the thermoplastic matrix to form the abrasive filament;
(b) a means to secure the plurality of abrasive filaments together to form a brush construction.
The filaments of the invention can be incorporated into brushes of many types and for myriad uses, such as cleaning, deburring, radiusing, imparting decorative finishes onto metal, plastic, glass substrates, and like uses. Brush types include wheel brushes, cylinder brushes (such as printed circuit cleaning brushes), mini-grinder brushes, floor scrubbing brushes, cup brushes, end brushes, channel brushes, flared cup end brushes, circular flared end cup brushes, coated cup and variable trim end brushes, encapsulated end brushes, pilot bonding brushes, tube brushes of various shapes, coil spring brushes, flue cleaning brushes, chimney and duct brushes, and the like. The filaments in any one brush can of course be the same or different. A nonlimiting list of exemplary brushes in which the plastic particle filled filaments can be used include brushes such as described in U.S. Pat. Nos. 5,016,311, 5,083,840, and 5,233,719 (Young et al.), and U.S. Pat. No. 5,400,458 (Rambosek), the entire disclosures of all of which are incorporated herein by reference.
In another form of the brush embodiment, the brush is a unitary injection molded brush. The brush can be as described in co-pending U.S. Pat. No. 5,679,067, xe2x80x9cMolded Abrasive Brushxe2x80x9d, (Johnson et al.). Johnson et al. discloses an integrally molded abrasive brush for rotary tools, comprising a generally planar flexible base having a first side and a second side, and a plurality of bristles extending from the first side of the base. The bristles have an aspect ratio of at least 2 and are integrally molded with the base. The molded abrasive brush comprises a thermoplastic matrix which includes abrasive particles interspersed throughout at least the bristles. The bristles extend generally perpendicular to the base, parallel to the axis of rotation of the molded abrasive brush.
Another form of a unitary injection molded brush is disclosed in U.S. patent application Ser. No. 08/559,334, xe2x80x9cRadial Brush Segment,xe2x80x9d (lonta et al.), filed even date herewith and assigned to the assignee of the present application. lonta et al. discloses a molded brush segment having a plurality of integrally molded bristles extending from a generally planar center portion. The brush segment is molded from a thermoplastic matrix which includes a plurality of abrasive particles interspersed throughout at least the bristles. The molded brush segments can be generally circular, with the bristles extending radially outward in the plane defined by the central portion. A plurality of brush segments can be combined to form a brush assembly.
The third embodiment of the present invention pertains to a method of refining a workpiece surface. The method comprises the steps of:
(a) providing a workpiece having an outer surface,
(b) providing an abrasive brush, wherein the abrasive brush comprises:
(i) abrasive filaments comprising plastic abrasive particles distributed in the thermoplastic matrix to form the abrasive filament;
(ii) a means to secure a plurality of abrasive filaments together to form a brush construction; and
(c) moving the brush relative to the workpiece to remove a portion of the workpiece outer surface.
A variation on the third embodiment is a method comprising:
(a) providing an abrasive brush comprising:
(i) a plurality of abrasive filaments comprising plastic abrasive particles distributed in a thermoplastic matrix, and
(ii) means to secure said plurality of abrasive filaments together to form the brush;
(b) contacting the plurality of abrasive filaments against a workpiece surface, wherein the workpiece surface includes a foreign material thereon, and
(c) moving the abrasive brush relative to the workpiece to remove the foreign material from the workpiece surface. In some instances the abrasive brush will remove a portion of the underlying workpiece while removing the foreign material. In other instances, the abrasive brush will not remove a significant amount of material of the workpiece outer surface.
Other aspects and advantages of the invention will become apparent from the detailed description which follows.